Melanin concentrating hormone (MCH) neurons are present in the hypothalamus and have been implicated in various behaviors. To study the role of these neurons in sleep, MCH neurons were selectively stimulated via the gene for the light-sensitive cation channel, channelrhodopsin-2, which was inserted into the MCH neurons of wild-type mice. Three weeks later MCH neurons were stimulated for 1 min every 5 min for 24 h. A 10 Hz stimulation at the start of the night hastened sleep onset, reduced length of wake bouts by 50%, increased total time in non-REM and REM sleep at night, and increased sleep intensity during the day cycle. Sleep induction at a circadian time when all of the arousal neurons are active indicates that stimulation of melanin concentrating hormone neurons can powerfully counteract the combined wake-promoting signal of the arousal neurons. The authors suggest that this could be potentially useful in treatment of insomnia.

Konadhode RR, Pelluru D, Blanco-Centurion C, Zayachkivsky A, Liu M, Uhde T, Bailey Glen Jr W, van den Pol AN, Mulholland PJ, Shiromani PJ: Optogenetic Stimulation of MCH Neurons Increases Sleep. J. Neurosci. 33(25): 10257-10263 (2013).

http://www.jneurosci.org/content/33/25/10257.abstract?etoc